Switching device for solenoid switch

ABSTRACT

The circuit arrangement for an auxiliary relay that actuates a starting relay for a starter device of an internal combustion engine includes a temperature measuring device (20) and a control and/or regulating circuit device (16,16&#39;) for controlling, in a turned-on state, an operating current (I) flowing through a relay coil of the auxiliary relay according to a temperature of the auxiliary relay or starting relay measured by the temperature measuring device (20) so that the operating current (I) and mean value of the operating current (I) are controlled according to the temperature. The control and/or regulating circuit clocks the operating current and can vary the duty cycle to reduce the power losses.

BACKGROUND OF THE INVENTION

The invention relates to a circuit arrangement for a starting relay fora starter of an internal combustion engine.

In motor vehicles, it is known to use starting relays for a starterdevice of an internal combustion engine. These starting relays are usedto switch a high current with a relatively low control current. The highcurrent (starter current, necessary for turning over an engine by meansof a starter), amounts to as much as approximately 1000 A in passengercars, for instance. The current flowing during the starting process viathe relay coil of the starting relay, by comparison, is about 80 to 100A, for instance. This relatively low current compared with the startercurrent is still too high, however, to be switched directly via astarting switch (ignition lock) or via an electronic control unit. Tothat end, it is known from German Patent DE 37 37 430 C, among othersources, to assign the starting relay an auxiliary relay, which isactuatable by means of the starter switch of the motor vehicle. Onedisadvantage is that for the additional auxiliary relay not only mustadditional installation space in the motor vehicle be made available;besides, this relay is one additional consumer with a correspondinglyhigh power loss.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a circuitarrangement of the above-described type which eliminates theabove-described disadvantages.

According to the invention, the circuit arrangement for an auxiliaryrelay that actuates a starting relay for a starter device of an internalcombustion engine includes a temperature measuring means and controland/or regulating circuit means for controlling, in a turned-on state,an operating current flowing through a relay coil of the auxiliary relayaccording to a temperature measured by the temperature measuring meansso that the operating current and mean value of the operating currentare controlled according to the temperature of the auxiliary relay orthe starting relay.

The circuit arrangement according to the invention offers the advantagethat the auxiliary relay can be optimized, that is, reduced with respectto its structural size in particular, so that less installation spacehas to be made available. Because a control and/or regulating circuit isprovided that varies the operating current of the auxiliary relay, it isadvantageously possible to vary the operating current of the auxiliaryrelay as a function of selectable criteria in such a way that for everyoperating state of the auxiliary relay its operating current assumesonly the actual magnitude necessary, so that the power loss occurring atthe auxiliary relay is reduced as greatly as possible. It thus becomespossible to integrate the auxiliary relay with the starting relay,producing a compact structural unit.

In an advantageous feature of the invention it is provided that thecontrol circuit includes a clocked control or current regulatingcircuit; via the clock frequency and/or the duty cycle, the magnitude ofthe operating current can be fixed as a function of certain operatingstates of the auxiliary relay. This advantageously makes it possible toadapt the operating current of the auxiliary relay to varying operatingconditions, such as an operating temperature and/or an armature positionof the auxiliary relay. By means of this optimal adaptation of theoperating current to each operating state of the auxiliary relay, thepower loss of the auxiliary relay is reduced. This is the result inparticular of a lowering of the operating current, once the armature ofthe auxiliary relay has attracted, or has just begun its motion alongits path of motion. It is also advantageous that by optimal controlledclocking of the operating current of the auxiliary relay, it is possibleto set a constant high mean operating current value under variousoperating conditions, and especially various temperature conditions. Itshould be taken into account that at different temperatures, on the onehand the characteristic curve of a retraction spring for the armature ofthe auxiliary relay and on the other the magnetization behavior of theauxiliary relay and the ohmic resistance of the coil vary, with theconsequence that the operating current of the auxiliary relay varies aswell. As a rule, the coil of the auxiliary relay should be dimensionedin accordance with the maximum incident operating current. However, bycontrolling the auxiliary relay operating current in accordance with theinvention it becomes possible to operate the auxiliary relay at a lower,constantly high, clocked mean operating current value, so that thevarious operating conditions can be responded to via a choice of aset-point current value, a clock frequency, and/or the duty cycle. Bythis means, the coil can now be designed for the maximum current at thehighest operating temperature.

Further advantageous features of the invention will become apparent fromthe other characteristics recited in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in further detail below in exemplaryembodiments in conjunction with the associated drawings. Shown are:

FIG. 1, a schematic block circuit diagram of a circuit arrangementaccording to the invention;

FIG. 2, a diagram of the course of the set-point and actual value of theoperating current of the auxiliary relay for the embodiment of FIG. 1;

FIGS. 3-6, several signal courses for various duty cycles of the clockedoperating current of the auxiliary relay;

FIG. 7 a second exemplary embodiment of the circuit arrangementaccording to the invention; and

FIG. 8, a diagram of the course of the set-point and actual value of theoperating current for the auxiliary relay according to the embodiment ofFIG. 7.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a circuit arrangement, identified overall by referencenumeral 10, for a device for starting an internal combustion engine. Thecircuit arrangement 10 has a turn-on element 12, such as an ignitionlock or starting switch, that is connected to an electronic control unit14. The electronic control unit 14 has a control circuit 16 for anauxiliary relay 18 connected to the control unit 14. The control circuit16 is also assigned a temperature detection circuit 20, which isconnected to temperature sensors, not shown here, that are disposed inthe vicinity of the auxiliary relay 18 or in the engine compartment. Thecontrol circuit 16 includes a trigger stage 19, acting as a Schmitttrigger, whose response values a) and b) are variable, and which sensethe current course at the output of the control unit 14.

The control unit 14 has further circuit elements, not relevant here,that are necessary for the function of the motor vehicle. Switchcontacts, not shown here, of the auxiliary relay 18 are connected to thewindings of a starting relay 22; its switch contacts, likewise notshown, turn the main current circuit of a starter device 24 on and off.

The mode of operation of the circuit arrangement 10 will be brieflyexplained, referring to the merely schematic drawing. On actuation ofthe turn-on element 12, the coil of the auxiliary relay 18 is suppliedwith current via the electronic control unit 14. Supplying the currentto the auxiliary relay 18 is effected, in a manner to be describedhereinafter, via the control circuit 16 for the operating current of theauxiliary relay 18. The switch contacts of the auxiliary relay 18connect the relay coil of the starting relay 22 to an operating voltage,so that the armature of the starting relay 22 closes the main currentcontacts of the starter device 24 and connects them with a voltagesource, which in a motor vehicle is as a rule the vehicle battery. Viathe main current contacts of the starter device 24, the relatively highstarter current now flows; it can amount to approximately 1000 A. Viathe switch contacts of the auxiliary relay 18, which connect the relaycoil of the starting relay 22 to the voltage source, a switching currentat the level of about 80 to 100 A flows. Via the coil of the auxiliaryrelay 18, the operating current I of up to 40 A flows, being varied bythe control circuit 16 of the control unit 14.

In FIG. 2, the set-point value and actual value of the operating currentare shown in the exemplary embodiment for controlling the operatingcurrent I of FIG. 1. The set-point value I_(soll) of the operatingcurrent is lowered to a lower value at time t2 by the control circuit16. As a result, the actual value of the operating current, I_(ist),shown in simplified form on the left, is established. This takes intoaccount the physical facts that for retention of the armature of theauxiliary relay 18, a lesser magnetic flux density than what is requiredto attract the armature suffices. By lowering the operating current I byabout 50%, the power loss can be reduced to about 25%, since for theclosed magnetic circuit a lesser current is adequate for the requisitemagnetic flux density. This lesser operating current I flows through thecoil resistance of the coil and thus generates a lesser power loss, inthe form of heat energy, compared with the higher operating current Iprior to time t2.

The specific layout of the control circuit 16, which on the one handperforms the clocking of the operating current I in the control unit 14and on the other lowers the operating current I, is not to be addressedin detail here. However, besides the trigger stage 19, it also includesa timer stage for the time t2 for switchover of the trigger stage fromthe higher response values a1 and b1 for turn-off (a1) and turn-on (b1)of the operating current I_(ist) to the lower response values a2 and b2.In this example, after t2, which is approximately 30 ms long, theset-point value of the operating current I is lowered from 25 A to 12 A.For the control circuit 16, the use of well known multivibrators,precision Schmitt triggers or other suitable oscillator circuits,preferably including microprocessors, is attractive. The time period t2until the current is lowered should be specified such that the relayarmature will reliably lift away from its position of repose at anearlier time t1. Via the temperature detection circuit 20 it is possibleto lower the limit values of the operating current I_(ist), via thevariable response values a and b of the trigger stage 19, as thetemperature increases. Moreover, the time period t2 until the reductionof the operating current can thus also be shortened as the temperatureincreases. In this way it is possible to compensate for thetemperature-dependent friction of the relay armature in motion andoptionally for a temperature-dependent spring force of the armaturerestoring spring.

In FIGS. 3-6, signal courses for clocking the operating current I areshown. The signal course can be represented here by exact rectangularsignals with an accurate duty cycle or in other words clock frequency.For furnishing the rectangular signals, the control circuit 16 may forinstance include suitably designed function generators. In FIG. 3, forinstance for a clock frequency of 2 kHz, the signal course is shown witha 30% duty cycle; that is, with reference to one unit of time (period),the operating current I is on for 30% of this unit of time while it isoff for the remaining 70%. Accordingly, FIG. 4 shows a signal coursewith a 60% duty cycle, FIG. 5 a signal course with a 90% duty cycle, andFIG. 6 a signal course with a 100% duty cycle. Depending on the dutycycle chosen, the result is an area encompassed by the course of theline of the operating current I and thus, in a known manner, the energysupplied to the coil. The lower the clocking or in other words theon/off duty cycle chosen, the lower is the energy supplied and thus thepower loss occurring in the coil.

By means of the clocking of the operating current I, it is thus alsopossible to vary the duty cycle as a function of certain operatingparameters of the auxiliary relay 18. For instance, the duty cycle canbe varied as a function of an operating temperature of the auxiliaryrelay 18 in order to maintain the specified operating current intensity.At the same time, lowering the operating current I can be accomplishedvia a reduction of the duty cycle, or it can be varied as a function oftemperature.

Hence by a trigger stage 19 of the control circuit 16, with duty cycleschosen here merely as examples, the operating current I for an auxiliaryrelay 18 at the moment it is turned on can be acted upon forapproximately 30 ms with a 60% clocking, while at time t2 (FIG. 2) theduty cycle is changed to 30%. Thus by simple generation of therectangular signals of the trigger stage 19, the energy demand of thecoil of the auxiliary relay 18 can be reduced drastically. By couplingthe control circuit 16 to the temperature detection circuit 20, theclocking of the operating current I can be adapted in a simple way towhatever operating conditions prevail. For instance, it is expedient fora cold relay to furnish the operating current I with 60% clocking at themoment the relay is turned on and 30% clocking at time t2. For anauxiliary relay 18 at its normal operating temperature, the duty cycleat the moment it is turned on may amount to 90%, while at time t2 it ischanged over to 50%. For a heated auxiliary relay 18, for instance, theclocking can be done at 100% at the turn-on moment, while a change to60% clocking takes place at time t2. By means of the control circuit 16and the temperature detection circuit 20, the time t2 for the changeoverof the duty cycles can moreover be varied. For instance, for a coldauxiliary relay 18 the time t2 can be 30 ms; for a normally heatedauxiliary relay 18, time t2 can be 25 ms, and for a heated auxiliaryrelay 18, the time t2 can be 15 ms.

It thus becomes clear that by means of the duty cycle and the instant ofswitchover of the duty cycle between the attraction range and theretention range of the auxiliary relay 18, triggering of the auxiliaryrelay 18 that enables a drastic energy savings is possible.

Overall, an operation of the auxiliary relay 18 can thus be establishedat a constant mean operating current value despite varying operatingconditions and especially varying operating temperatures. Moreover--asnoted--a reduction in the power loss of the auxiliary relay 18 isaccomplished by the clocking of the operating current I.

By means of the constant mean operating current value under varyingtemperature conditions, the possibility arises of exerting influence onthe structural embodiment of the auxiliary relay 18. On the one hand, itbecomes possible to increase the spring force of the restoring springfor the armature of the auxiliary relay 18, since the auxiliary relay 18no longer needs to be designed for the least favorable operatingsituation to be expected, namely the maximum operating current I at themaximum temperature. By increasing the spring force for the armature ofthe auxiliary relay 18, the tendency of the switch contact to bounce canbe reduced, making it possible to increase the service life of thecontacts. Another advantage is that by this increase in spring force andhence reduction in the tendency to bounce, it becomes possible toincorporate the auxiliary relay 18 into a housing of the starting relay22. The accelerations or impacts at the starting device that occurduring the switching operations of the starting relay 22, which can bein ranges up to from 5000 to 10,000 g can thus better be intercepted bythe stronger spring force of the restoring spring of the auxiliary relay18.

Moreover it is also possible, in the event that it is undesirable formajor spring forces to have to be overcome, to reduce the coil windingof the auxiliary relay 18, since less energy input overall is necessaryfor function. Because as a result less installation space is required,better integration of the auxiliary relay 18 into the starting relay 22is also made possible.

Clocking of a starter auxiliary relay is possible not only with the aidof the control circuit explained in conjunction with FIGS. 1 and 2; itcan also be attained with a control and regulating circuit as in FIGS. 7and 8. There, the operating current of the control relay is clocked by aregulator 17 via a clocking stage in the control unit 14' in such a waythat the mean current value established in connection with the isregulated to a predetermined set-point value I_(soll). To that end, theactual value of the operating current I_(ist), which varies continuouslybecause of the clocking, is sensed at the auxiliary relay 18. The dropin the set-point value can now be accomplished as a function of timeafter the turn-on of the relay or with the aid of a further sensor 21and the connected control circuit 16' as a function of the position ofthe auxiliary relay armature.

As shown in the accompanying graph (FIG. 8), it is contemplated thatbefore the onset of motion of the relay armature, regulation is done tothe set-point current Is1, and to the lesser set-point current Is2 whenthe armature is in motion and to the even lower set-point current Is3when the relay armature is fully in its track.

The winding is designed such that at 0° C. and with regulation to Is1,for instance, a duty cycle of 60% is reliably adequate for a relayarmature motion (duty cycles at an identical relay armature location andIs2 at 40%, for example and at Is3 20%, for example). At the maximumwinding temperature (+100° C., for instance), at the relay currentsregulated as above, because of the higher winding resistance, a dutycycle of 100% results at Is1 (66% at Is2, 33% at Is3).

The relay current is accordingly regulated fundamentally independentlyof interfering variables (such as temperature, battery voltage, etc.)but in dependence on the status of the relay armature (position, speed,for instance) and on the demand for magnetic force. The duty cycle isautomatically correctly set by the regulator.

Overall, the result is thus a relay current regulation dependent on therelay armature force requirement, having the following advantages inparticular:

thermal relief

reduced impacts on armature contact, reduced bouncing

increased functional safety (higher armature attraction force)

increased relay service life

We claim:
 1. A circuit arrangement for an auxiliary relay that actuatesa starting relay for a starter device of an internal combustion engine,said circuit arrangement comprising a temperature measuring means (20)and a control and/or regulating circuit means (16,16') for controlling,in a turned-on state, an operating current (I) flowing through a relaycoil of the auxiliary relay according to a temperature measured by thetemperature measuring means (20) so that the operating current (I) and amean value of the operating current (I) are controlled according to saidtemperature, wherein said temperature measuring means (20) is arrangedso that said temperature is that of the auxiliary relay (18) or thestarting relay (24).
 2. The circuit arrangement as defined in claim 1,wherein the control and/or regulating circuit means (16,16') includes aclocking stage for a clocked current circuit.
 3. The circuit arrangementas defined in claim 1, wherein the control and/or regulating circuitmeans (16,16') has a trigger stage (19) for clocking the operatingcurrent (I) with a certain variable duty cycle.
 4. The circuitarrangement as defined in claim 3, wherein the duty cycle of theoperating current (I) is variable over time.
 5. The circuit arrangementas defined in claim 3, wherein the control and/or regulating circuitmeans (16,16') includes means for lowering the operating current (I) toa lowered operating current after a predetermined time (t2) has beenreached.
 6. The circuit arrangement as defined in claim 5, wherein themeans for lowering the operating current (I) lowers the operatingcurrent (I) after starting motion of an armature of the auxiliary relay(18) from a rest position or when the armature reaches an operatingposition thereof.
 7. The circuit arrangement as defined in claim 5,wherein the lowered operating current has a lower duty cycle than theoperating current (I) prior to the lowering by the means for lowering.8. A circuit arrangement for an auxiliary relay that actuates a startingrelay for a starter device of an internal combustion engine, saidcircuit arrangement comprising a temperature measuring means and acontrol and/or regulating circuit means (16,16') for controlling, in aturned-on state, a duty cycle of an operating current (I) flowingthrough a relay coil of the auxiliary relay according to a temperaturemeasured by the temperature measuring means (20) so that the operatingcurrent (I) is lowered when said temperature increases, wherein saidtemperature measuring means is arranged so that said temperature is thatof the auxiliary relay (18) or the internal combustion engine.
 9. Thecircuit arrangement as defined in claim 8, wherein the control and/orregulating circuit means (16,16') lowers the duty cycle of the operatingcurrent at a variable time (t2) and means for determining said variabletime (t2) according to said temperature of said auxiliary relay (18) orsaid internal combustion engine.
 10. The circuit arrangement as definedin claim 8, wherein the control and/or regulating circuit means (16,16')controls the duty cycle of the operating current according to anarmature position of the auxiliary relay (18).
 11. The circuitarrangement as defined in claim 8, wherein the control and/or regulatingcircuit means (16,16') has a trigger stage (19) for clocking theoperating current and controls the operating current (I) of the relaycoil so that a required attraction force is produced at a maximumallowable operating temperature when the duty cycle of the operatingcurrent is 100%.
 12. The circuit arrangement as defined in claim 8,wherein the control and/or regulating circuit means (16,16') has atrigger stage (19) for clocking the operating current and lowers theoperating current (I) from a first set-point value (I_(soll)) to atleast one additional lower set-point value after a time (t1, t2, t3).13. The circuit arrangement as defined in claim 12, wherein the controland/or regulating circuit means (16,16') lowers the operating current(I) in two steps according to a turn-on time (t1,t2) or an armatureposition of the auxiliary relay (18).